Developing novel drugs for chronic pain management — both more effective and less addictive than opioids — will reduce the number of patients at risk of opioid dependence.
Chronic Pain and the Opioid Crisis
More than 25% of Americans suffer from chronic pain. This is on par with adults from equivalent regions; between 10-25% of adults in other western countries experience chronic pain, while some estimates of chronic pain incidence among adults in the United Kingdom are as high as 50% of the population1.While chronic pain incidence is similar in Europe, Canada, and the United States, opiates are more widely prescribed — and abused — in the US.
Opioids have been found to be relatively ineffective for treating chronic pain conditions, often leading to tolerance and hyperalgesia with long term use2,3.
Furthermore, long term use of opioids for chronic pain has directly contributed to the opioid crisis in the US: as new prescribing standards are instituted, patients seek black market pills and heroin to manage their pain.
This cycle of ineffective use, dependence, and drug abuse can best be addressed through developing more effective and less addictive treatments for chronic pain.
The Call for Novel Pain Management Therapeutics
Dr. Tom Price, Secretary of the US Department of Health and Human Services, stated that his agency will pursue five main strategies to combat the opioid epidemic:- Increase access to addiction recovery treatment.
- Promote access to overdose-reversal drugs.
- Increase public health surveillance.
- Provide support for current research on addiction.
- Encourage better pain management practices4.
Examples of this work include:
- Development of compounds which activate different opiate receptors than traditional opioid drugs5.
- Identification of new plant-derived compounds for management of chronic pain6,7,8,9.
- Compounds which complement opiate efficacy, such as gabapentin, thus requiring smaller doses of opiates for similar efficacy10.
- Adding abuse deterrents or making extended release formulas for existing drugs.
- Development of new opioids with fewer adverse effects11.
Chronic Pain Management Research
To develop new therapeutics, researchers seek to better understand and model pain more effectively in preclinical experiments. It is just as critical to model the development of tolerance and potential for abuse, all of which require predictive animal models.Animal Models of Chronic Pain
There are various methods to classify pain, such as by the level of intensity (mild to severe), by duration (acute to chronic), or by the cause of the pain (such as neuropathic or nociceptive).Animal models of chronic pain are generally classified as inflammatory, neuropathic, visceral, or nociceptive (in mechanical and thermal models).
- Examples of inflammation models used for studying pain include induced models of arthritis, utilizing either Complete Freund's Adjuvant or Type II collagen.
- Visceral pain models typically involve injection of an irritant into the intraperitoneal cavity.
- The most commonly used models of neuropathic pain are surgical models including partial sciatic nerve ligation, sciatic nerve ligation, and chronic constriction injury.
Conclusion
Discovery of new therapeutics for managing chronic pain is of vital importance for reducing opiate abuse. Mouse and rat models play a key role in understanding pain signaling and pathways, as well as the mechanisms of dependence and addiction.Rodent models are the most commonly used in pain studies as they are small, relatively inexpensive, and feature a variety of well-defined models for studying various aspects of pain and treatment.
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